Coilable waveguide



May 21, 1968 G. LEHNERT 3,383,895

COILABLE WAVEGUIDE Filed Aug. 11, 1965 VIII/lll u INVENTOR. @UNT/mEH/VERT y BY a@ www United States Patent O 3,383,895 COILABLE WAVEGUIDEGnther Lehnert, Hannover-Bothfeld, Germany, assigner to HackethalDrahtund Kabel-Werke Aktiengesellschaft, Hannover, Germany Filed Aug.11, 1965,"Ser. No. 478,905 5 Claims. (Cl. 72-198) ABSTRACT OF THEDISCLOSURE Apparatus for converting a spirally corrugated waveguideoriginally formed from metal tubing of circular cross-section to acorrugated waveguide of elliptical cross section in a continuous andprecise manner.

In the generation and transmission of microwaves it may be necessary toguide the wave energy over nonrectilinear paths. Up to the present,coaxial cables were generally used as flexible coilable conductors fortransmission of polarized electromagnetic waves of high frequency, ie.,the lower frequency microwaves. However, at very high frequencies, i.e.,higher frequency microwaves, coaxial cables have too great anattenuation factor to permit economic transmission of wave energy.Therefore, attempts have been made to employ corrugated waveguides ofcircular cross-section as flexible conductors for very high frequencywaves. In order to obtain suflicient mechanical exibility of such awaveguide, the corrugations must be made correspondingly deep. However,these deep corrugations either generate undesired modes of oscillationsor else cause an appliedpolarized wave to split into two components. Thecorrugations, in addition, produce rotation of the directions ofpolarization of an applied polarized wave. The amount of rotationdepends upon the length and curvature of the guide and the frequency ofthe waves. Furthermore, in transmission of a wave with a wide frequencyband, very bad depolarization occurs, making withdrawal of the appliedwave energy impossible without incurring heavy losses in the availableenergy.

It has been proposed to reduce depolarization and corresponding loss ofenergy in such circular corrugated wave guides by sectionally deformingthe guide cross-section into ellipscs or to rotate two sections ofidentical waveguides with respect to each other in the direction ofpolarization. It is apparent that such measures are time consuming andunreliable and make the mounting of such round waveguides verydifficult.

Attempts have been made to make the well known rectangular waveguideexible by providing notches in its walls or by inserting flexiblesections. In such cases undesired discontinuities result, and awaveguide of rectangular cross-section is hardly coilable withoutserious deformation of the cross-section.

It is accordingly an object of the invention-to provide a coilablewaveguide for the transmission of very high frequency electromagneticwaves.

It is another object of the invention to provide a corrugated waveguidewhich minimally depolarizes polarized electromagnetic waves transmitteddown the waveguide.

It is a further object of the invention to provide a coilable corrugatedwaveguide which is on the one hand relatively inexpensive to fabricateand on the other hand is a highly efficient and reliable in the transferof very high frequency polarized electromagnetic waves.

Broadly, the invention is based on the possibility of using certain wavetransmission modes in elliptic waveguides for transmission ofelectromagnetic wave energy.

In accordance with an aspect of the invention, there is contemplated theprovision of a longitudinally seam 3,383,895 Patented May 21, 1968 ICCwelded, helically corrugated hollow tube of elliptic crosssection as acoilable corrugated waveguide for transmission of polarizedelectromagnetic waves of very high frequency, and particularly fortransmission of a linearly polarized H11 type of wave.

It should be noted that such an elliptic waveguide can be Voptimallymatched to the cross-section of apparatus coupled to the guide(particularly of rectangular crosssection) by proper choice of the ratioof large to small ellipse diameters, pitch and depth of thecorrugations.

It should also be noted that measurements have shown that for such awaveguide the boundary values and depolarization of the electromagneticwave to be transmitted are substantially equivalent to conditionsprevailing in a rectangular waveguide with a corresponding ratio ofsides.

1t should be further noted that because of the transverse rigidity ofthe elliptic waveguide the mechanical and electrical properties remainunchanged after repeated coiling, provided that the radius of curvatureof the coil turns is not too small.

Another aspect of the invention is the method of making the waveguidesimply and continuously by a procedure wherein a flat metal strip isformed into a circular tube, the abutting edges welded together and thetube then helically corrugated. Subsequently, the tube passes throughsuitable means in which its cross-section is deformed to an ellipticsection. The tube is then, optionally, provided with a wear resistant,synthetic resin outer sheath and coiled on a reel.

In order to insure a uniform tube cross-section so as to preventtransmission discontinuities and associated electromagnetic wavereections, uniform forming without bends and creases is essential.Therefore, according to a feature of this aspect of the invention, thereis provided a roller system comprising two balanced wheels withdiameters much larger than the diameter of the tube to be formed. Thewheels are provided with peripheral grooves corresponding to theelliptic cross-section of the tube being deformed. The wheels rotatefreely and are mounted in a plummer block vertically above one anotherso that they touch each other in the horizontal plane through the tubeaxis.

Other objects, features and advantages of the invention will be apparentfrom the following detailed description when read with theaccompanyingdrawings which show by way of example and not limitation in:

In the drawing,

FIG. l is a schematic showing of an apparatus for making waveguides inaccordance with the invention;

FIG. 2 is an enlarged cross-section on the line 2-2 of FIG. 1;

FIG. 3 is an enlarged cross-section on the line 3-3 of FIG. 1; and

FIG. 4 is a sectional View taken on the line 4-4 of FIG. 1.

Referring now to FIG. 1, a flat metal strip 2 is moved by suita-bletransport means generally indicated at S from the supply roll 1 and isprogressively formed into a tube of circular cross-section on formingtable, including curved shaping elements, not shown, all in a well knownmanner. The longitudinal abutting edges of the tube are welded atwelding station S, preferably `by an electric arc. The tube so obtainedis corrugated helically in conventional corrugator 6. The helicallycorrugated tube 7 of circular cross-section enters the ellipticalcross-section forming apparatus 8 through a circular inlet bushing 11and is elliptically deformed therein. The elliptical crosssectionedwaveguide 9, upon -leaving outlet channel 12 is sheathed with a wearresistant synthetic resin coating applied at a spraying station K and isthen coiled on a takeup reel 10. The coating may be polyethylene,polyvinylchloride or similar plastic synthetics with or without fillers.

The sprayed on coating preferably fills the troughs of the corrugationsto provide a perfectly smooth surfaced conduit.

The elliptical cross-section forming apparatus 8 comprises a pair ofparallel plummer blocks 17 mounted on standards A in a vertical positionand supporting two balanced forming wheels 13 and 14, having diametersmuch greater than the diameter of the corrugated tube 7. For the purposeof deforming the corrugated circular crosssectioned tube into anelliptical cross-section, the periphery of forming wheels 13 and 14 areprovided with grooves 13A and 14A of corresponding cross-section (FIG.4). Wheels 13 and 14 are mounted vertically above each other in such amanner that they almost or actually Contact each other at a peripheralpoint in the horizontal plane through the longitudinal axis of thecorrugated tube 7. Grooves 13A and 14A each have the shape of half anellipse, so that the minor axis of the ellipse is preferablyperpendicular, i.e., in a plane including a line joining the axes ofrotation of forming wheels 13 and 14 as shown in FIG. 4. Alternatively,the major axis of the ellipse could be so disposed, but then there isgreater danger of creasing the corrugated tube or forming a non-uniformelliptic section.

As mentioned above, the corrugated tube 7 must be elliptically formed asuniformly as possible. Ideal forming of the tube would be accomplishedif the diameters of wheels 13 and 14 were infinite. This obviously isimpossible, but the ratio of diameters of forming wheels 13 and 14 andcorrugated tube 7 should be as large as possible. Experiments have shownthat a ratio of greater than 40:1 is adequate to provide uniformdeformation of the circular to elliptic sections.

Wheel bearings 15 and 16 in the plummer blocks 17 are verticallyadjustable by means (not shown) in a well known manner, in order toadjust the position of the wheels 13 and 14 to that of the tube 7 and toadjust the spacing of the wheels within limits for forming differentelliptical cross-sections. In order to prevent chang or scratching ofthe corrugated tube 7 in the entrance or inlet bushing 11 or exit oroutlet channel 12, both are made of or lined with wear resistant, smoothsynthetic material, such as high molecular polyethylene.

The so formed elliptical cross-sectioned corrugated waveguides arecoilable without change of mechanical and electrical characteristicswhen coiled. Accordingly, such a waveguide is particularly applicablefor use in radar. When used in rigid mountings, such as an antenna feedline in a transmitter tower, and similar applications, the cableaccording to the invention can be paid olf from the supply reel at theconstruction site and then cut off when the proper length has :beenfound. It is then only necessary to provide the necessary input andoutput matching couplers. Flexing and curving of the waveguide have noinfluence on the electric characteristics of the cable. The waveguide ofthe invention can even be used to advantage as compared withconventional waveguides, when two directions of polarization are to lbesupplied to an antenna. The laying of two waveguides as provided by thisinvention is always simpler and less expensive than the laying of tworectangular waveguides or a single circular waveguide, which mustbe`perfectly compensated and matched after laying and thereby requiretime consuming additional work.

There has thus been shown a helically corrugated waveguide of ellipticalcross-section, as well as a method for making such a waveguide, which iseasily coilable and which has outstanding electrical properties andwhich minimally depolarizes polarized very high frequencyelectromagnetic waves. In addition, as a feature of the invention,particular elliptical cross-section forming apparatus has been shownwhich produces uniformly formed waveguides with a minimum possibility ofintroducing undesired creasing or chafing to the guide.

There will now be obvious to those skilled in the art many modificationsand variations which satisfy many or all of the objects but which do notdepart from the spirit of the invention as defined in the appendedclaims.

What is claimed is:

1. Apparatus for making tubular waveguides comprising a source ofhelically corrugated hollow metallic tubing having a substantiallycircular cross-section and given diameter, means for moving said tubinglongitudinally, an inlet guiding means for guiding said tubing tolongitudinally move with its longitudinal axis along a given line, apair of deforming wheels, means for supporting said deforming wheels tofreely rotate with their rotational axes at a fixed distance from eachother and their peripheries substantially in contact with each other ata point in a plane including said given line in a region downstream fromsaid inlet guiding means, each of said deforming wheels having in theperiphery thereof a peripheral groove with a cross-section of one halfof an ellipse, an outlet guiding means downstream from said deformingwheels for guiding said tubing along said given line when exiting frombetween said deforming wheels and reel means for taking up said tubingas it leaves said outlet guiding means.

2. The apparatus of claim 1 wherein the diameters of said deformingwheels are at least forty times the diameter of said tubing.

3. The apparatus of claim 1 wherein the minor axis of the half ellipseof the cross-section of said peripheral grooves is parallel to a linejoining the axes of rotation of said deforming wheels.

4. The apparatus of claim 1 wherein said inlet guiding means is abushing with a guiding port of substantially circular cross-section forslidably accommodating said tubing and said outlet guiding means is achannel shaped member.

5. The apparatus of claim 4 wherein Said inlet and outlet means have atleast tubing bearing surfaces of a wear resistant synthetic material.

References Cited UNITED STATES PATENTS 1,849,973 3/1932 Buchwald 72-187FOREIGN PATENTS 451,472 9/ 1949 Italy. 372,899 12/ 1963 Switzerland.

RICHARD J. HERBST, Primary Examiner. L. A. LARSON, Assistant Examiner.

